Please write an email to the UK concerned authority stating that you are the wife of the deceased person and requesting for death certificate or copy of the death certificate. I hope they immediately issue the same to you. there may be some charges, which they may let you know.

If your in-laws had registered his death to the local municipal authority then only you will be getting the death certificate from the local municipal authority.

Death Certificate and Burning (Cremation/ Burial) Certificate are two different things, When his cremation is being done in India then it is a general process from the cremation center to take original death certificate and issue a Burning Certificate by Municipal Corporation. You can apply before local municipal corporation for same.

if the cremation is done in india and if the death certificate had been got from the corporation then you can visit the corporation website and you can download the copy of death certificate by providing the required details

Hi 1) The municipal authorities wherein the last rites of your sister's husband was done will definitely issue you a copy of death certificate (as your sister's husband died in UK and his last rites were conducted in India) alternatively2) Since your sister's husband died in UK and the last remains were transported to India, you can approach the Indian Embassy in UK for the death certificate. 3) Alternatively, your sister can approach the local district court and request the court for a) issue of legal heir certificate and b) copy of death certificate.

All three options are available to you and you can choose the one that is convenient to you.